Foundry core



' this class.

Patented Nov. 10, 1931 UNITED STATES PATENT OFFICE ROBERT EARL, .13., OFUTICA, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COM- IPANY, A CORPORATIONOF NEW YORK FOUNDRY coma No Drawing.

The present invention relates .to foundry cores and molds which areemployed for the casting of metals and alloys, and which ordi benefitscan be obtained in the fabrication of foundry external molds,particularly in the treatment of mold surfaces hich come into contactwith molten metal. For the sake of brevity I will use the term coresgenerally herein to indicate external as wellasinternal members employedin the casting of metals.

A core for metal casting purposes must withstand the erosive or cuttingaction of the molten metal which is being cast and must hold togetherduring the casting operation for a sufficient length of time to permitthe molten metal to acquire a set. On the other hand, an ideal coreshould disintegrate after the metal has been cast so as to be readilyremovable from the solidified cast metal object.

veniently classified as non-heat-hardening and heat-hardening. Linseedoil is an example of a common non-heat-hardening bond. Rosin and othernatural resins also have been used as core bond and belong to Linseedoil bonded cores are baked to accelerate their hardening b oxidation butthis is not heat-hardening 11E3 fhe ed to the heat of the cast metal.

Cores bonded by means of a Iron-heat-hardening bond or adhesive do notwell withstand the erosive or cutting effect of molten metal,

such as steel or iron. As a consequence seriousdefects are present inthe finished casting due to the local disintegrationof the core andimbedding of core material in pockets in the casting adjacent the core.The sand, or other core material, also adheres to and becomes im-Application iled. January 17, 1930. Serial No. 421,655. I

bedded in the entire surface of contact of the cast metal and the core.In many cases expensive chipping of the casting and filling in ofcavities by local deposition of fused metal .is required. An'organiccarbonizable core bond consisting of such material as linseed oil leavesa hard carbbn residue in the sand and hence the carbonized core isremovable only with great diificulty. Unless the cross- Section of thecore is so small that the carbon is more'or less burned out, it must .bechipped or broken out of the casting. Its adherence to (the castingmakes cleaning of the casting very laborious and expensiv p In the case,of some castings, particularly large castings, an inorganicheat-hardenin bonding agent such as clay has been foun necessary toimpart sufficient strength to the coreemployed. While cores so bondedbetter withstand the erosive efiect of hot metal,

hard, brick-like material which is removable only with extremedifiiculty from castings. 'Power drills are required in most cases torecores to be employed in the casting of metals Two classes of corebonds WlllCh have been employed in common practice may be conare bondedwith an organic heat-hardening material which at the tem erature of themolten metal is decompose Such a bond forms a hard, erosive-resistingbody which is capable of maintaining its strength and coherence duringthe initial period of the cast-- ing operation or until the molten metalhas filled the mold and taken the" initial set.

Thereafter, as it is subjected to the high tem-,

f perature of the hot casting metal, it becomes '70 they become hardenedby heat into a very without other reacting ingredients. r, The

bonding agent preferably isem loyed in solutionas hereinafter described.p

s The preferred embodiment of my invention mav be present, as forexample monobasic acids-such as the acids derived from vegetable oils,and in particular the acids derived from castor oil or linseed oil.

In some cases an alkyd resin may be employed as a bond in which rosin,or other natural resin, is substituted for a part of the organic acidingredient. A vegetable oil,

such as Chinawood oil, may in part replace 7 the acids derived from adrying oil in the resin composition. Other alcohols may be used in placeof g1 cerine, either polyhydric ormonohydric. or example, ethyleneglycol may be substituted for part of the glycerine. In some cases, aresin may be prepared suitable for the purposes of my invention bycombining or'associating a vegetable oil with a resin made from apolyhydric alcohol and a plolybasic acid, as described for example, in

. S. Patent 1,739,447 issued Dec. 10, 1929.

In the preparation of foundry cores embodying my invention a suitablecore mate rial, such as sand, zirconia, alumina, or the like, is mixedwith an alkyd resin in suitable proportions, the resin preferabl beingin solution, the mixture then being ormed into cores by knownmethods,'and baked to produce an initial set of the bond. I have usedsuccessfully a resinous composition made up as described in BritishPatent 284,349 accepted Sept. 20, 1928, replacingin part the drying oilacid entering into composition described in this patent with Chinawoodoil, using if desired also a small percentage of rosin.

As solvents, various ordinary organic solvent liquids, may be employed,as for example, naphtha, toluol, acetone, or denatured alcohol. I preferto employ a mixture in substantially equal proportions of kerosene andcrude coal tar distillates comprising crude toluol, crude xylol or crudesolvent naphtha. Such crude solvents contain some tar and in some casesnaphthalene. A small proportion of tarry material gives added hardnessand strength to cores bonded with alkyd resin. Kerosene acts as alubricant.

The following is an illustrative example of the fabrication of myimproved core. About 50 arts by weight of core sand and one part o a'solution, containing by wei ht about 4 parts of an alkyd resin, and preerably an alkyd resin containing rosin as well as a drying oil acid,together with about 6 parts of solvent, are thoroughly mixed to form amolding composition. These proportions may be varied to suit conditions.In some cases a small amount of an adhesive cereal binder may be addedtothe sand. For example about 1250 to 1300 pounds of core sand may be putinto a sand mixerand given green strength by the addition of cerealbinder, such as fl'our or Mogul which is a corn product. About 23 poundsof an alkydresin solution of the proper viscosity, then are added andthe entire mass is thoroughly mixed.

In some cases an unmodified alkyd resin, made from glycerine andphthalic anhydride in molecular proportions may be employed as a binder,a suitable solvent being employed, although the modified resin has beenfound to be superior.

invention is formed into a core 0 desired shape, the core is baked at atemperature of about 350 F. to drive off solvent and to cause the resinpartly to be converted from the sol to the gel state to render the corehard and capable of resisting heat without fusion or softening. Thelength of time requiredfor baking varies with the size of the core, itsshape and other conditions. In some cases the core need be baked foronly 15 or 20 minutes while in other cases several hours may berequired. The length of the baking period is in any case much shorterthan is required when employing such bonding agents as linseed oil,especially in the case of large cores. Complete conversion of the alkydresin during the baking period to the most highly polymerized state isnot required as such a core bond is further hardened and heat convertedby contact therewith of the molten metal.

It is not necessary that in the entire mass of the core the bond shouldhave been given a set or that all of the solvents should have beenremoved in the interior portion prior to the use of a core for castingpurposes as the heat of the molten cast metal will complete the removalof solvent and will further polymerize the bond.

When molten steel,iron, brass, or other high heat cast material comesinto contact with cores embodying my invention the first effect of themolten material is, I believe, to make the heat-convertible binder stillstronger and harder by further polymerization. Whatever the true actionmay be it is a fact that the core withstands the heat and erosive actionof the cast metal sufliciently long to avoid trouble from prematurebreakdown. Thereafter the core reaches the break-down point of the bond,and the disintegration and volatilization of the bond leaves the sanddry and loose.

In some cases, particularly in the fabrication of large cores, 2. facingof a suitable refractory material such as silica sand, prefiredgraphite, orv fine carbon. which is free from combined water or othervolatile matter bonded with clay may be applied upon the surface ofcores further to strengthen After a molding mixture embod ing my'pension o eanna the cast metal. Such a facing may be applied byspraying on the mold, either on a green sand mold or a-dry sand mold orcore, a susf carbon silica flour or other ,suitable refractor in asolution'of a suitable a d resin. The interior mass of the core which isbonded with alk d resin, or other bond which is capableof eingdecomposed at high temperatures, then may be easily shaken out of thecasting and the clay-bonded facin then may be more easily removed thanbe thecase werethe entire core claywould bonded.

My improved cores not only have eater cohesion, hardness, and greater manical stren th initially than cores made with the use 0 bindersformerly employed, but they retain their shape until the cast metal hastaken an initial set. The are not out by hot flowing metal under conitions which would cause complete failure of similar cores bonded withanon-heat convertible material. The cores have a smooth, hardsurface'which withstands erosion by the cast metal and against which thecast metal will closely lie thus producing castings of accurate surfaceconfiguration; O

A most striking advantage of cores embodyin my invention results fromthe volatility e? the binder when in contact with the hot metal. Asabove indicated, when internal cores are employed which are imbedded inthe cast metal, the binder is so completely volatilized by the hot metalthat the sand, or other body material of the core,

is leftin such loose state that it may be readily poured, or blown, outof the completed casting. My improved cores vent more readily, that is,release gas more evenly and the amount of as produced is not great. Blowholes are t erefore practically eliminated.

' Practically no illv smelling or otherwise obnoxious gases or fumes aregiven oil from my improved core bond either during casting or when thecore material is removed from the casting, thereby conducing to thecomfort and health of the workmen.

The'cores also are more resistant to moisture and can be stored forlonger periods without warping or disintegration. As the cores aremechanically stronger and harder, breakage in handling and in storage isreduced. The reater strength of members made in accor ance with myinvention makes it possible to dispense partly or wholly with.reenfo'rcing rods which ordinarily are required in the case of large orcomplicated cores.

These advantages of the improved cores embodying my invention can-beobtained without additional cost and in fact the costis found in manycases to be materially lower than with cores made with other types ofbonding agents. One of the savings eflected required for baking thecores and t e de-,

creased cost of equipment in ovens and core ans which is required.Another saving is ue to the lower breakage or loss of cores by we ing. ny Y T e ease with which the, cone may be shaken or blown out of thecasting results in a material saving of labor and time and facilitatesthe introduction of line production methods into-the foundry. The timesaved in removing the core may run from several to many hours withasaving in direct labor alone of many dollars for a single casting. Thereduction in time in making the core and roducing the completed castinready for shipment in an emergency, invo ves an indirect saving which itis impossible to estimate.- Material savings also are effected ,by thereduction'of losses due to spoiled castings and the saving of laborformerly requlred in patching castings containing sand pockets. 1

. For the fabrication of cores embodying my invention, sand from usedcores can be used over again. In fact, it is possible to again useso-called burned sand without My new form of bond is also applicable toexternal metalcasting members. Here tofore, only so-called green sandmolds have been believed to be .pr acticable for external casting molds,that is, molds made from sand containing a natural bond. In accordancewith my invention dry sand is mixed with a solution of alkyd resin asabove described. The mixture is molded with a pattern in an externalmolding container to make an external mold of relatively small sectionwhich is then baked as above described. The baked mold may be insertedin a suitable container and carried by a conveyor to the cupola wherethe casting may be poured. Upon solidification the cast metal ob ect maybe cleaned from the adhering disinte rated mold material in any suitableway as, or example, in a tumbler or by a sand blast. l

What-I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A composition for making foundry cores comprising a comminuted corebody material suitable therefor, a binder constituted of a polyhydricalcohol-polybasic acid condensation product which is capable ofbeingeconand the constituents of which are largely volatilizable at thetemperature of the molten metal for the casting of which such cores areintended and a volatile solvent therefor.

2. A strong, coherent casting core comprising a preponderant amount of acomminuted refractory material and a material cementing said particlescomprising a heat-hardening resin which is capable of being volatilizedat the fusion temperature of metal intended to be cast into contact withsaid core, and which containsin chemical combination glycerine andphthalic acid or its anhydride.

3. A foundry core for casting metals comprising a refractory materialand an alkyd resin bond therefor. 1

4. A foundry core for casting metals comprising a refractory materialand an alkyd resin bond therefor in a heat-hardened state.

5. A core for castin metals comprisinga core body and a bon thereforconstituted of a polyhydric alcohol-polybasic acid resin conltlaining afatty acid in combination therewit 6. A core for casting metalscomprising a acid resin containing in chemical combination a drying oilacid.

,. asaaaao mixed with a. core body comprising an alkyd resin containinga vegetable oil acid, Chmawood oil, a crude volatile solvent and kero-.

' ROBER EARL, JR.

core body and a polyhydric alcohol-polybasic r ing cores which consistsin admixing sand with a solution of an alkyd resin, forming said cores,and baking at a temperature at which the solvent is eliminated and saidresin is rendered hard and capable of resisting heat without fusion.

9.- The process of fabricating cores for metal casting which consists inadmixing a comminuted core body material with a solution of an alkydresin which is capable of being heat-hardened into a strong, hard, heat-.resisting state, and is capable of bei'ng disintegrated at a highertemperature, shaping said mixture into desired form, and baking the sameat a temperature of about 350 F. to remove the solvent and toheat-harden the binder then flowing a fused metal into contact with saidcore at a temperature sufliciently high to eventually disintegrate saidplastic material and render the core body capable comprising an alkydresin containing a fatty acid and a crude volatile, organic solvent. g

12. A core bond which is adapted to be

